During the past ten years, casting by squeezing has been extensively used for the production of large-size castings with a wall thickness of 2 to 5 mm which is about the wall thickness of the finished part or item.
The basic principle of casting by squeezing is as follows. As mold halves or parts of a split-type mold are brought together, most of the melt filling the metal receiving chamber is forced through the feeding chambers into the molding chamber where the casting is produced.
The quality of the casting thus produced is largely dependent on the level of molten metal in the molding chamber and the speed at which it is driven into that chamber at any given moment of time during the period when the mold halves are brought together. Thus the quality of the casting is largely dependent on the level of molten metal in the metal receiving chamber just before the mold halves are brought together. Deviation in the level of melt in the metal receiving chamber from an optimum value are due to imperfections in the melt feeding system and a change of the cubic content of the metal receiving chamber which may occur during its service life.
Casting by squeezing is done in molds comprising detachable parts which include a flat or cylindrical base and mold halves at least one of which is mounted on the base so that it can move along the base or in the radial direction without losing contact with the base. Thus the mold halves can be driven apart and brought together. The detachable parts of the mold also include cheeks adjacent to the base and mold halves in the zone of their parting line. The internal surfaces of the base, mold halves and cheeks form a chamber in at least one of the mold halves, which is divided by projections into a lower, metal-receiving chamber, side, feeding chambers and a central, molding chamber. The chambers communicate with one another. For the production of shell-type castings, the base is provided with a special core (cf. V. N. Vinogradov, "Liteyniye formy dlya tsvetnykh splavov"/"Casting Molds for Non-Ferrous Alloys"/, Machinostroyeniye Publishers, Moscow, 1981, pp. 35 and 37).
In a casting machine, the base of the split-type casting mold is secured in the center on the bed. The mold halves are mounted on cross-pieces coupled to the end supports of the bed by means of guides and drives for driving the mold halves apart and bringing them together. In order to seal the parting line between the mold halves and the bed, the cheeks are mounted on one of the mold halves or on additional supports provided on the bed so that said cheeks can be set in reciprocating or angular motion. The drive, by means of which the mold halves move on the cross-pieces, is provided with a locking means. The latter is put into operation when the mold halves are brought into abutting, or end-to-end, relation. If both mold halves are movable the drive is provided with a means for synchronizing their movement. The drive is also provided with a special device to control the speed at which the mold halves are brought together.
The level of melt in the metal receiving chamber is controlled with the aid of calibrated ladles and different devices, such as magnetodynamic proportioners.
The time lag of such devices and the build-up of metal are factors which affect the accuracy of proportioning. Another such factor is a change of the volume of the metal receiving chamber which is due to build-up of metal, wear of the lining, and periodic expansion and compression of its walls as they are heated and cooled during operation. Until recently, it has been impossible to have a level of melt in the metal receiving chamber just before the mold halves are brought together, which would ensure a desired level of melt in the molding chamber and the rate at which it is forced into that chamber, i.e., would satisfy the conditions essential for the production of high-quality castings with a high-strength, homogeneous, structure.